As the analysis in Section III reveals, temporal
changes in the screen cost energy. When the screen changes color,
the CPU consumes additional energy to generate data for the
framebuffer, the framebuffer has to be then updated, and
corresponding liquid crystals have to change orientation. The
second experiment was designed to measure the energy of iPAQ1 for
changing the screen from black to different colors. To eliminate
the additional energy due to the LCD presenting different colors,
it is turned off. Therefore, the experiment mainly accounts for
the additional energy due to the first two of the three processes
mentioned above. The data are presented in Table IX.
It demonstrates the more the color changes, in terms of (R,G,B)
components, the larger the additional energy consumption. This
implies that a GUI with a constant color theme will be more
energy-efficient than one that often changes color.

Table IX:
Additional energy for showing and hiding windows of
different colors on a black background